High methane emissions from an anoxic fjord driven by mixing and oxygenation

Tracking sources, sinks and long-term trends of methane emissions is imperative under climate change. Marine methane fluxes remain elusive and uncertain even though the ocean plays a major role in global budgets. High-latitude fjord ecosystems are widespread, store large amounts of sediment carbon, and undergo cycles of water column mixing, making them potential but still overlooked sources of methane to the atmosphere. Here, state-of-the-art benthic lander robots and multi annual observations revealed that anoxic fjords emit substantially more methane during mixing events than under water stratification. Fjords only cover 0.1% of global sea surface area, but may contribute as much methane as that released by the open ocean, which covers 84% of the global sea surface.